The origins and timing of HIV spread into the U.S. remain in question. One possibility is that alterations in the virus' genetic makeup led to its current pathogenic properties, but a similar virus may have been transported from Africa where HIV is endemic. We have screened approximately 6000 plasmas from missionaries travelling between Africa and the U.S. between 1968 and 1983. Although the group may be considered low risk for sexually transmitted diseases, they are a group with high casual contact with the African people. Approximately 200 plasmas were found to be positive on ELISA screening but none was found to have HIV specific proteins detected by Western Blot. Further analysis of the HIV proteins are being carried out. Selected plasmas are being screened for related virus, including HTLV1.